Chemical Compatibiliser

It is also well known that using any of the compatibilisation methods causes a decrease in the interfacial tension between the continuous and dispersed phases. The impact of different compounds largely depends on their chemical composition and structure, or the concentration used in the case of chemical compatibilisation. It was found in previous work that hydrogen bonds, n - electron, ion or dipole interactions are mostly developed between two or more components of immiscible phases [54, 55]. Furthermore, the lack of groups which are available for chemical interaction is generally the cause for incompatibility. However, Sionkowska and co-workers also noted that there are specific cases in which two or more polymers were capable of miscibility in the solvent phase, but after evaporation of the solvent the immiscible phases remained [45, 54]. 

Another well-known case is when only chemical interactions exist between the dispersed phase, the polymer or polymer matrix material and the compatibiliser. One of the criteria of chemical compatibilisation is the existence of free functional groups, which can react with each other during compatibilisation. It is important to note that the presence of free functional groups is not often associated with the development of chemical interactions due to steric hindrance reasons the compatibilising functional groups, matrix and functional groups of the dispersed phase cannot react with each other, i.e., the interactions occur at the boundaries. One typical example of chemical compatibilisation is the so-called in situ functionalisation. In this case, surface modification of the matrix and dispersed phase occur first, and then the modified surfaces are linked via in situ connections [51-53, 75, 76]. 

For general aspects on sonochemistry the reader is referred to references [174,180], and for cavitation to references [175,186]. Cordemans [187] has briefly reviewed the use of (ultra)sound in the chemical industry. Typical applications include thermally induced polymer cross-linking, dispersion of Ti02 pigments in paints, and stabilisation of emulsions. High power ultrasonic waves allow rapid in situ copolymerisation and compatibilisation of immiscible polymer melt blends. Roberts [170] has reviewed high-intensity ultrasonics, cavitation and relevant parameters (frequency, intensity,... 

Usually polymeric substances of appropriate chemical structure and morphology which promote the miscibility of incompatible materials. Block copolymers are especially useful surfactants at the polymer/polymer interface because the two blocks can be made up from molecules of the individual polymers to be mixed. Typical compatibilisers in polymer blends are LDPE-g-PS in PE/PS CPE in PE/PVC acrylic- -PE, -PP, -EPDM in polyolefin/PA and maleic-g-PE, -PP, -EPDM, -SEBS in polyolefin/polyesters. 

Blends of poly (ethylene terephthalate) (PETP) and polypropylene (PP) with different rheological properties were dry blended or compounded, and extrusion foamed using both physical blowing and chemical agents, and the foam properties compared with those of foam produced from the individual components in the absence of compatibilisers and rheology modifiers. The foams were characterised by measurement of density, cell size and thermal properties. Low density foam with a fine cell size was obtained by addition of a compatibiliser and a co-agent, and foamed using carbon dioxide. The presence of PP or a polyolefin-based compatibiliser did not effect... 

Diblock copolymers, especially those containing a block chemically identical to one of the blend components, are more effective than triblocks or graft copolymers. Thermodynamic calculations indicate that efficient compat-ibilisation can be achieved with multiblock copolymers [47], potentially for heterogeneous mixed blends. Miscibility of particular segments of the copolymer in one of the phases of the bend is required. Compatibilisers for blends consisting of mixtures of polyolefins are of major interest for recyclates. Random poly(ethylene-co-propylene) is an effective compatibiliser for LDPE-PP, HDPE-PP or LLDPE-PP blends. The impact performance of PE-PP was improved by the addition of very low density PE or elastomeric poly(styrene-block-(ethylene-co-butylene-l)-block styrene) triblock copolymers (SEBS) [52]. 

It is concluded that IR spectroscopy provides information on qualitative as well quantitative analyses of rubbery materials, apart from their microstructures (that is, whether cis or trans, syndiotactic, atactic or isotactic). Different types of rubber blends (compatibilised or self-crosslinked) can be identified by the infrared spectroscopy. Synthesis, and degradation of polymers can also be followed by IR spectra. Mechanism of interaction between rubbers and fillers, can also be studied by IR-spectra. Different types of chemical reactions like the milling behaviour of rubbers, mechanism of adhesion and degradation can also be studied with the help of IR spectroscopy. The technique plays a great role in the product analysis under reverse engineering. 

Polycaprolactone aliphatic polyesters have long been available from companies such as Solvay and Union Carbide (now Dow Performance Chemicals) for use in adhesives, compatibilisers, modifiers and films as well as medical applications. These materials have low melting points and high prices ( 4-7 per kg in 2005). PCL is predominantly used as a component in polyester/starch blends such as... 

In the field of thermoplastic immiscible blends, the emulsifying activity of block copolymers has been widely used to solve the usual problem of large immiscibility associated with high interfacial tension, poor adhesion and resulting in poor mechanical properties. An immiscible thermoplastic blend A/B can actually be compatibilised by adding a diblock copolymer, poly(A-b-B) whose segments are chemically identical to the dissimilar homopolymers, or poly(X-b-Y) in which each block is chemically different but thermodynamically miscible with one of the blend component. Theoretical... 

Thus, it appears that chemical reactivity or ionic-cross interactions could lead to in situ compatibilising or miscibility enhancement during melt-mixing. However, several questions remain. How does the reactivity modify the thermodynamic balance, the reciprocal miscibility or the rheological behaviour of the melt Or, how the covalent or ionic bonding influence the interfacial adhesion processability and final mechanical properties of the immiscible blends ... 

The chemical structure of polyamides and polyester involves only few chances for a reactive compatibilisation during melt processing with short residence times... 

A highlight of the reactive compatibilisation of extremely incompatible polymers is the chemical bonding between the anti-adhesive PTFE and the polar polyamides. It had been assumed for a long time that a chemical bonding between PTFE and polyamide is impossible because there was no appropriate reaction mechanism. PTFE is a highly crystalline polymer which could only be processed by using special equipment. The utilisation in tribological systems is a well-known... 

Due to its non-polar chemical structure, PP interacts poorly with the typically pwlar fillers such as CaC03, and optimum dispersion is normally difficult to achieve. Compatibilisers are frequently used to improve the interfacial adhesion between CaC03 and PP, in order to gain the envisaged enhancement in mechanical properties (Fuad et al, 2010). Bi-functional molecules such as maleic-anhydride grafted PP (PP-g-MAH) are commonly used as compatibilisers for PP and CaC03 (Roberts Constable, 2003). 

Reactive blending is an important method for the compatibilisation of polymer blends. Two or more immiscible polymeric components are functionalised with chemical units that are coreactive. During melt... 

Addition of p-cresol formaldehyde (PCF) into phenolic/NBR blends resulted in rednction in the domain size of the dispersed phase and improvement in mechanical properties [244]. PCF resin has an intermediate polarity compared with NBR and resole and can react faster with NBR. Therefore, PCF molecules are likely to be concentrated at the phenolic/NBR interface and act as an external compatibilising agents [245]. Thus compatibility and chemical bonding between NBR and phenolic resin is improved, leading to the enhancement in properties. The other materials used as toughening agents of phenolic resin include elastomers such as natural rubber and nitrile rubber [246, 247], reactive liquid polymers [248] and thermoplastics such as polysulfone, polyamide, polyethylene oxide [249, 250]. 

More than one compatibiliser may be required to achieve success in all these respects. Both physical and reactive chemical mechanisms may be involved. It is not always desirable to... 

Functionalisation, or compatibilisation by chemical reaction techniques, usually involves mixing one of the polymers, say A, with a small quantity of chemically modified (functionalised) polymer A, or a chemically modified polymer compatible with A. The chemical modification introduces maleic, methacrylate or similar groups, chosen to react chemically with, or at least promote, compatibility with B. 

ExxonMobil Chemical s Exxelor compatibilisers include maleated PP and maleated elastomeric ethylene copolymers. They improve the impact strength of wood plastics composites, but there needs to be at least 50% wood in the composition to see the full effect. They also improve the water absorption and allow the wood content to be increased from 50% to 60%, giving better mechanical properties with no net increase in materials costs. Some of these additives are also recommended for use in polymer blends such as PA/ABS or PA6/PA6-6. 

Compatibilisers are certain to benefit from the recycling trend, but the reuse of polymers for plasties (as opposed to their use as fuel or their conversion to feedstock for chemical intermediates) may be aeeompanied by the reuse of at least a proportion of the additives. Researeh is being earned out to make possible the systematic recovery of additives from used artieles. Several observers believe that energy recovery and feedstock recycling will often be more eeonomie than eonversion to second-life plastics products. 

Free radical grafting of maleic anhydride (MA) onto polyolefins has gained wide industrial use. MA modified polyolefins are an essential part of many plastics formulations. They are used as chemical coupling agents, impact modifiers, and compatibilisers for blends and filler reinforced systems [65-67]. 

Polybond 1001 (PP-AA), a polypropylene functionalised with 6% w/w acrylic acid, was supplied by BP Chemicals Limited. The functionalised compatibilising agents, FC1, FC2 and FC3, were synthesised from PP-AA. An example is given in Figure 1. Further details are published elsewhere (20). 

Blends used to create MFCs can be separated into two broad categories those containing two condensation polymers that will cause a self-compatibilisation effect in the composite, and those requiring the addition of a compatibilizer if a chemical reaction between the constituent polymers is desired. For example, blends combining polyesters with polyamides fall into the former category while blends containing a polyolefin component belong to the latter. 

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